Machines for compression molding closure shells, or compression molding sealing liners within closure shells, typically include a turret or carousel that rotates around a vertical axis. A plurality of molds are provided around the periphery of the carousel, in the form of male and female mold sections that are aligned along vertical axes parallel to the axis of rotation. Cams drive one or both of the mold sections of each pair between an open position, in which a molded part is stripped from the male mold section and a charge of plastic material is placed in the female mold section, and a closed position in which the male and female mold sections are brought together to compression mold the shell or liner. In a liner machine, premade shells are placed in a nest when the mold sections are open, and a charge or pellet of liner material is placed within the shell before the molds are closed. U.S. patents that illustrate machines of this type for compression molding plastic closure shells include U.S. Pat. Nos. 5,670,100, 5,989,007, 6,074,583 and 6,478,568. U.S. patents that illustrate machines of this type for compression molding sealing liners within closure shells include U.S. Pat. No. 5,451,360.
Although vertical axis carousel-type machines of the noted type have enjoyed substantial commercial acceptance and success, innovation remains desirable. In particular, in vertical axis carousel-type machines, the mold forces and the weight of the rotating equipment are parallel to the vertical axis of rotation, creating a bending moment with respect to the axis of rotation and the bearings and shaft that support the carousel. Carousel-type machines also require a substantial amount of valuable floor space in a manufacturing facility. It is a general object of the present disclosure, in accordance with one aspect of the disclosure, to provide a method and apparatus for compression molding plastic articles, such as plastic closures and plastic liners within closure shells, which reduce the forces applied to the support frame and bearings, reduce maintenance requirements and the amount of energy needed to operate the machine, and/or reduce the amount of floor space required per machine.
The present disclosure involves a number of aspects or inventions, which may be implemented separately from or in combination with each other.
A compression molding machine in accordance with a first aspect of the present disclosure includes a wheel mounted for rotation around a horizontal axis and a plurality of angularly spaced molds disposed around the wheel. Each of the molds includes a first mold segment and a second mold segment disposed radially outwardly of the first mold segment. Each of the second mold segments is movable radially with respect to the associated first mold segment between a radially inner closed position with the first mold segment for compression molding a plastic article, and a radially outer open position spaced from the associated first mold segment for removing a molded article from the mold and placing a mold charge into the mold.
In some preferred embodiments of the disclosure, a cam is disposed adjacent to the wheel for moving the second mold segments radially inwardly and outwardly in sequence as the wheel rotates around its axis. Each of the molds may include an abutment for engagement by the second mold segment as the second mold segment is moved radially outwardly from the associated first mold segment, and a stripper coupled to the abutment for stripping molded parts from the first mold segment. There preferably is lost motion between the second mold segment and the abutment to allow the second mold segment to clear the first mold segment before stripping. In other embodiments of the disclosure, the stripper is operated by a cam independently of motion of the second mold segment. Back-up springs, such as coil or fluid springs, preferably are disposed between the first mold segments and the wheel for absorbing excess compression force applied to the first mold segment. The molds preferably are disposed in angularly spaced circumferential arrays on both sides of the wheel for balancing the forces applied to the wheel and by the wheel to its rotating mechanism. Each of the molds preferably includes a cam-operated latch for releasably locking the second mold segment to the first mold segment in the closed position of the mold segments.
A compression mold for molding plastic closures or plastic liners within plastic closures, in accordance with another aspect of the disclosure, includes at least one male mold segment having a mold core and a stripper sleeve surrounding the mold core. At least one female mold segment is aligned with the male mold segment. The female mold segment is movable with respect to the male mold segment between a closed position to form a mold cavity with the male mold segment, and an open position spaced from the male mold segment for removing a molded article from the cavity and placing a mold charge into the cavity. The stripper sleeve is operatively coupled to the female mold segment to move over the mold core and strip a molded part from the core as the female mold segment is moved away from the male mold segment. The stripper sleeve preferably is coupled to the female mold segment in such a way that there is lost motion between the stripper sleeve and the female mold segment to allow the female mold segment to clear the mold core before initiating motion of the stripper sleeve with respect to the core. The stripper sleeve is movable axially over the mold core in preferred embodiments of the disclosure. However, movement of the female mold segment also could impart rotary motion to the stripper sleeve to unthread a molded closure from the mold core, for example.
A method of compression molding plastic articles, such as plastic closure shells or plastic sealing liners within closure shells, in accordance with yet another aspect of the present disclosure, includes providing a wheel mounted for rotation around a horizontal axis and a plurality of angularly spaced molds around the wheel. Each of the molds includes a first mold segment and a second mold segment disposed radially outwardly of the first mold segment. As the wheel is rotated, each second mold segment in turn is moved radially outwardly with respect to the associated first mold segment and a plastic mold charge is placed between the mold segments. The second mold segment is then moved radially inwardly to a closed position with the first mold segment to compression mold the article. When the second mold segment is thereafter moved radially outwardly from the associated first mold segment, the molded article is removed from the mold prior to placement of a new mold charge between the mold segments. In one preferred method in accordance with this aspect of the disclosure, the outward motion of the second mold segment is used to remove the molded article from the mold.